EP3883743A1

EP3883743A1 - Method for manufacturing a plastic container equipped with a handle obtained using the boxing technique

Info

Publication number: EP3883743A1
Application number: EP19835450.8A
Authority: EP
Inventors: Camille GUITON
Original assignee: Sidel Participations SAS
Current assignee: Sidel Participations SAS
Priority date: 2018-11-20
Filing date: 2019-11-19
Publication date: 2021-09-29
Anticipated expiration: 2039-11-19
Also published as: FR3088572A1; EP3883743B1; WO2020104747A1; FR3088572B1; US20220009146A1; US11534952B2

Abstract

The invention relates to a method for manufacturing a container (1) using stretch-blow-moulding starting from a plastic preform inside a forming unit, the forming unit comprising a mould (2) a stretch rod (3) able to move heightwise inside the mould, the method comprising in succession a pre-blowing step (S1) and a blowing step (S2), the method also comprising a step (B) of boxing a handle, a phase of moving the stretch rod up being initiated before the blowing step, the boxing step being initiated after the stretch rod has been moved up, the handle being formed on the axis of extension of the stretch rod.

Description

Title: Method of manufacturing a plastic container provided with a handle obtained by boxing.

The field of the invention is that of the design and manufacture of plastic containers from preforms.

More specifically, the invention relates to a method and a forming unit for producing plastic containers, having a boxed handle centered on the container, which forming is carried out by stretch-blow molding of preforms.

Conventionally, a preform comprises a hollow body, generally cylindrical of revolution, a neck which constitutes the rim of the container to be formed, and a bottom which closes the body opposite the neck. The bottom is usually hemispherical or at least symmetrical in revolution with respect to the longitudinal axis of the preform.

To make a preform, an injection mold is used, which comprises an injection core (determining the shape of the interior of the preform) and an outer wall (determining the exterior of the preform). The internal volume determined by

the arrangement of the core and the outer wall determines the final shape of the preform. The plastic material constituting the preform is injected at a very high temperature (the material is fluid) and at a high pressure in the injection mold by a conduit which opens into this volume, through the outer wall, at a location of the wall centered on the bottom of the preform. This is why, at the end of their manufacture, the preforms comprise in the center of their bottom a point zone, called injection point.

The conventional technique for manufacturing a container from a preform consists in introducing the preform, previously heated to a temperature above the glass transition temperature of the material (about 80 ° C. in the case of PET), in a mold provided with a wall defining a cavity at the footprint of the container, and to be injected into the preform, by a nozzle, a fluid such as a gas (generally air) under pressure to press the material of the preform against the mold wall. Forming generally comprises a pre-blowing step during which the fluid is injected at a relatively low pre-blowing pressure (usually less than or equal to 15 bars), and a blowing step, subsequent to the pre-blowing step. -blowing, during which the fluid is injected at a high blowing pressure (usually greater than or equal to 20 bars and capable of reaching a pressure of the order of 40 bars).

Under the effect of the pressure, the material softened by the heating forms a bubble which swells and develops both in an axial direction, parallel to the main axis of the mold, and in a radial direction, perpendicular to the axis. main of the mold.

When the blowing is finished, a degassing step begins to evacuate the gas under pressure inside the container formed, until the interior of the container reaches a pressure equal to, or at least close to the pressure

atmospheric.

For the implementation of a stretch-blow molding manufacturing process, the forming unit comprises an elongation rod (also called stretch rod) intended to stretch the preform. This extension rod is movable in height inside the mold along an extension axis. The method then comprises a step of drawing the preform which successively presents a phase of descent of the rod

of extension to a low position, then a phase of raising the extension rod from its low position.

This elongation rod makes it possible to stretch the preform while avoiding any misalignment of the container formed. In this way, it ensures good mechanical strength and obtaining the desired aesthetics of the container.

More precisely, a distal end of the elongation rod pushes an area of the bottom of the preform, centered on the point of injection of the latter, until it comes to press this area against a bottom of the mold with the imprint. from the bottom of the container.

It should be noted that, in a conventionally known process, the initiation of the ascent phase of the extension rod takes place after a pressure peak in the blowing phase. The instant of initiation of the raising of the extension rod makes it possible to ensure that the injection point is well maintained by the extension rod until the container is formed, and thus to avoid a decentering of the bottom of the preform relative to the end of the rod, which would result in a poorly formed container.

It is recalled here that when a container is finished, there is generally in the center of its bottom the point of injection of the preform and an amorphous zone in the form of a pellet centered on this point. Indeed, it has been known for years that during stretching and blowing, the areas little or not stretched remain amorphous and the crystallization of the plastic material increases with stretching. However, since the elongation rod maintains the injection point, the center of the bottom of the preform corresponds to an area which is not stretched during the manufacture of the container;

the stretching and therefore the crystallinity increase as one moves away from the center. There is therefore, immediately around the center a little stretched area, therefore amorphous, which explains the presence of the mentioned tablet. The center itself is not at all stretched which explains why the injection point of the preform is found is found on the finished container.

Furthermore, a handle can be produced on the container during formation. For this, the mold then has inserts, called boxing inserts of a handle (for example two) movable through the walls of the mold.

The manufacturing process therefore includes a boxing step of a handle using the inserts, the handle being formed by bringing two portions of a wall of the container during its formation under the action of the boxing inserts. The boxing of a handle is initiated quickly during the process of manufacturing the container so that the boxing inserts deform the still softened plastic. Indeed, if this boxing step occurs too late in the manufacturing process and if the plastic material has started to cool, there may appear a phenomenon of over-stretching of the plastic material (for example PET) during the progression of the boxing insert of a handle.

On large and medium-sized containers, the handles are formed at the side of the container, that is to say in an off-center manner. The creation of a handle by boxing is however not easily achievable on small containers.

As shown in the various previously described steps of a manufacturing process, the presence of the extension rod prevents or limits the formation of a handle on a central part of the container, since the rod is located in the impact zone of the inserts, and the formation of a handle in the lateral part of the container may not be possible due to its small size.

The invention particularly aims to overcome the drawbacks of the prior art.

More specifically, the invention aims to provide a manufacturing method and a forming unit for manufacturing a container having a boxed handle that can be located on a central part of the container.

The invention also aims to provide such a method and such a forming unit which do not exhibit the phenomenon of over-stretching of the plastic material constituting the container.

The invention further aims to provide such a method and such a forming unit which allow the manufacture of a container at a rate identical to that of the containers according to the prior art whose handle is not centered on the container.

These objectives, as well as others which will appear subsequently, are achieved thanks to the invention which relates to a method of manufacturing a container by stretch blow molding from a plastic preform within a forming unit, the forming unit comprising:

- A mold defining an imprint of the container to be formed and comprising at least one boxing insert of a handle, each insert being movable through a wall of the mold;

- an elongation rod movable in height inside the mold along an extension axis and intended to stretch the preform,

the method successively comprising a pre-blowing step and a blowing step, the method also comprising:

- A step of stretching the preform successively comprising a descent phase, and a phase of raising the elongation rod along the extension axis;

a boxing step of a handle using the insert (s), the handle being formed by deforming at least one portion, called "deformed portion", of a wall of the container,

characterized in that:

- the phase of raising the extension rod is initiated before the blowing step;

- the boxing step is initiated after the lifting of the elongation rod above of a predetermined height along the extension axis on which the handle is formed, the handle being formed on the extension axis of the extension rod.

Of course, this process is also applicable to blanks, that is to say intermediate containers which have already undergone a forming operation but which are not in their final form.

Thanks to the manufacturing method according to the invention, it is possible to obtain a plastic container which has a gripping handle obtained by boxing and located on a central part of the container and in particular on the axis of extension of the rod. elongation inside the mold which defines the imprint of the container to be formed.

More specifically, the manufacturing process allows the creation of this handle while, for a manufacturing process according to the prior art, this creation is impossible because the elongation rod prevents or thwarts the deformation of the mold wall by the boxing insert (s) of a handle.

In fact, according to the invention, the elongation rod is raised before the blowing step (unlike the prior art where the phase of raising the elongation rod is initiated during the blowing phase). Thus, the boxing step of a handle, located on the extension axis of the elongation rod, can be initiated sufficiently early in the container manufacturing cycle when the plastic material is at a temperature suitable for boxing. A handle centered on the container can thus be created while avoiding over-stretching of the material

constituting the container.

In other words, by initiating the boxing step just after the raising of the extension rod above a predetermined height in combination with an initiation of the phase of raising the extension rod before the blowing step, this prevents the plastic material (for example PET) from falling below its glass transition temperature prior to boxing, and that the boxing inserts over-stretch said plastic material.

According to a preferred embodiment of the invention, during the boxing step of a handle, the deformed portion or portions enter a volume previously occupied by the extension rod in a low position between its descent phase and its ascent phase.

According to this embodiment, the deformed portion or portions can come into contact with the volume occupied by the extension rod before its ascent phase or exceed this volume.

In other words, the container thus has a portion deformed by boxing, forming the handle, which has a deformation depth such that it approaches, reaches or crosses the central axis of the container (which during the formation of the container in the mold coincides with the extension axis of the extension rod).

According to a preferred characteristic, the handle is formed by bringing two deformed portions of the container wall at least up to a maximum spacing, the maximum spacing being less than a minimum diameter of the extension rod.

The creation of such a handle, on a location occupied by the elongation rod during the stretch-blow molding step, is permitted by the method according to the invention because the elongation rod is raised before the blowing step.

Advantageously, the handle is formed by bringing the two deformed portions of the container wall up to a minimum distance called "air gap", the air gap being less than the minimum diameter of the elongation rod.

By bringing the two deformed portions as close to the wall of the container, a transparency effect may appear at the level of the handle. This effect of

transparency results from the fact that, after filling the container, even if the content of the container is colored, the very small spacing called "air gap" makes it possible to obtain a transparency effect through the two deformed portions of the wall and of the liquid located between these two portions.

According to a preferred solution, the ascent phase of the extension rod and the boxing stage are initiated during the pre-blowing stage.

In this way, it is favored a good deformation of the wall of the container which is at this stage of the manufacturing cycle at a temperature higher than the glass transition temperature of the plastic. This minimizes the risk that the boxing step is initiated when the material constituting the preform has started to pass below its glass transition temperature.

According to another preferred solution, the phase of raising the extension rod is initiated during the pre-blowing step, and the boxing step is initiated during the blowing step.

In this way, it is also possible to obtain a handle boxed on the extension axis of the elongation rod without the appearance of an over-stretching phenomenon of the plastic material.

According to an advantageous embodiment, the boxing step is initiated with the aid of a servo-control of the ascent phase of the elongation rod.

Such enslavement avoids the creation of interference between the boxing step and the stretching step of the preform. It is indeed essential that the elongation rod is raised beyond a predetermined height so that the boxing step can take place.

Advantageously, the predetermined height is located above a central boxing axis along which the insert (s) are movable, the central boxing axis being intersecting and perpendicular to the axis of extension of the elongation rod. .

With this design, it is with certainty that the boxing step by the insert (s) can be initiated because the predetermined height of rise of the extension rod is located beyond the central axis of boxing.

According to an advantageous characteristic of the method, the step of stretching the preform stretches the preform until its bottom reaches anti-slip means of an injection point of the preform, which are formed in the bottom of the mold.

It is then compensated for the fact that an early raising of the elongation rod can lead to a decentering of the preform during blowing.

Preferably, between the descent phase and the ascent phase, the elongation rod is kept in a low position along the extension axis for a duration D of between 5 milliseconds and 120 milliseconds, and

preferably between 20 milliseconds and 60 milliseconds. Compliance with these low and high values of duration D makes it possible to ensure that the preform injection point has been sufficiently centered inside the mold, and to optimize the operation of the actuators of the forming.

Respecting the duration D between 20 milliseconds and 60 milliseconds makes it possible to prevent the temperature of the preform from cooling below the glass transition temperature, for carrying out the boxing step (thus avoiding over-stretching of the material preform during the boxing stage), while ensuring a high production rate.

Preferably, the method of the invention is implemented on a rotary machine, which comprises a carousel and at least two molds, and the boxing step is initiated from an angular value DepBoxMin, in degrees, which corresponds to the angle traveled by a mold from an instant, called the start of the cycle, which angular value is determined using the following formula:

[Math 1]

in which :

- PT10 is an angular value in degrees of arrival of the elongation rod 3 in a low position;

- HT is an elevation height in millimeters of the extension rod from its low position allowing the release of a boxing volume from the handle;

- V is the ascent rate of the extension rod in millimeters / milliseconds;

- CAD is the rate of the mold in bottles / hour / mold.

The forming unit notably includes a carousel which carries the molds. The angular values are thus relative to the rotation of the carousel of the forming unit and more precisely to the angular position of the mold relative to a frame of the forming unit on which the carousel is movable in rotation.

According to this configuration, the initiation of the boxing step is optimized as a function of the predetermined ascent height of the elongation rod along the extension axis, the ascent speed, as well as the cadence of the mold.

The invention also relates to a forming unit for the manufacture of a container by stretch blow molding from a plastic preform, the unit forming including:

a mold defining an imprint of the container to be formed, the mold comprising at least one boxing insert with a handle, each insert being movable through a wall of the mold along at least one central boxing axis up to at a maximum boxing depth at which the insert defines a boxing volume of the insert inside the mold;

- an elongation rod movable in height inside the mold along an extension axis and intended to stretch the preform as a function of a path of descent and ascent of the elongation rod at the inside the mold,

characterized in that at least one of the boxing volumes of the insert extends around or opposite the extension axis of the elongation rod.

The forming unit naturally implements the method according to the invention.

Such a forming unit according to the invention thus makes it possible to manufacture a container by stretch-blowing which has a boxed handle around or opposite the axis of extension of the elongation rod, inside the mold. , without the transient presence of the extension rod inside the mold posing any problem or interfering with the trajectory of the boxing inserts. Indeed, the forming unit, then configured using the method according to the invention, allows the creation of such a boxed handle thanks to an early rise of the elongation rod compared to techniques according to art prior.

According to a preferred characteristic, the elongation rod and its trajectory define a volume of temporary occupation of the elongation rod inside the mold, at least one of the boxing volumes of the insert interfering with the volume of temporary occupation of the extension rod inside the mold.

Other characteristics and advantages of the invention will appear more clearly on reading the following description of a preferred embodiment of the invention, given by way of illustrative and nonlimiting example, and of the appended drawings among which:

[Fig. 1] is a schematic representation according to a cross-sectional view of a container obtained by the manufacturing method according to the invention and thanks to the forming unit according to the invention, as well as a representation of two boxing inserts d 'a handle positioned on either side of the container; [Fig. 2] is a front view of the container obtained by the manufacturing process and by the forming unit according to the invention;

[Fig. 3] is a schematic representation according to a cross-sectional view of a mold of a forming unit according to the invention;

[Fig. 4] is a representation of the course of the manufacturing process according to the invention, illustrating the sequence of process steps in relation to a pressure curve inside the container to be formed, with a curve illustrating the stroke of the rod. elongation inside the mold of the forming unit, as well as with a time axis.

Referring to Figure 3 the forming unit allows the manufacture of a container 1 by stretch blow molding from a plastic preform (or blank).

According to FIGS. 1 and 3, the forming unit comprises:

- A mold 2 defining an imprint of the container 1 to be formed;

- an elongation rod 3 movable in height inside the mold 2.

As illustrated in FIGS. 1 and 3, the forming unit, as well as the manufacturing method according to the invention, make it possible to manufacture a container 1. This container 1 takes in particular the form of a bottle.

The container 1, illustrated in FIGS. 1 and 2, has a wall 10, a handle formed by boxing thanks to the deformation of at least one portion called "deformed portion 100", of the wall 10 of the container 1, and a bottom 1 10, comprising a vault 120 surrounding a pellet 130 made of amorphous material and in the center of which is found, as explained in the preamble to the present application, the injection point 140 of the preform used to form the container 1.

By boxed “handle”, it is understood that the container 1 has in its volume at least one hollow or depression shape facilitating its gripping.

Thus, with reference to FIGS. 1 and 2, the two deformed portions 100 each form a depression relative to the general shape of the container 1. These depressions face each other and allow a person to position their hooked fingers to improve the grip of the container 1. As explained above and with reference to Figures 1 and 3, the mold 2 defines an imprint of the container 1 to be formed.

Mold 2 includes:

- a wall 20;

- two 200 boxing inserts with a handle.

Each of the boxing inserts 200 is movable through the wall 20 of the mold 2. More specifically, the inserts 200 are movable along a central boxing axis Xb up to a maximum boxing depth.

At this maximum boxing depth, the inserts 200 each define a boxing volume 201 of the insert 200 inside the mold 2. Each of these inserts 200 thus makes it possible to push back the wall 10 of the container 1 to form a deformed portion 100 and allow the appearance of the handle.

Referring to Figures 1 and 3, the elongation rod 3 is movable in height inside the mold 2 along a longitudinal axis Xe displacement, also called extension axis Xe.

This elongation rod 3 is intended to stretch the preform from which the container 1 is formed.

This elongation rod 3 stretches the preform as a function of a path of descent and ascent of the elongation rod 3 inside the mold 2 and along the extension axis Xe.

According to an implementation, not shown, the mold 2 may have means for preventing the injection point 140 of the preform from sliding. These anti-slip means are supported by the bottom of the mold 2. These anti-slip means can for example take the form of a cavity for receiving the plastic material stretched by the rod 3 of elongation. They can cooperate with complementary means of the elongation rod 3.

During the descent, then of the ascent of the elongation rod 3 inside the mold 2, and more precisely when the elongation rod 3 is in a low position (position reached between a descent phase E1 and a ascent phase E2 inside the mold 2), the elongation rod 3 defines a volume 30 of temporary occupation inside the mold 2.

According to the invention, at least one of the boxing volumes 201 of the boxing insert 200 extends around or opposite the axis Xe of extension of the elongation rod 3.

Indeed, the handle of the container 1 is formed on the axis Xe of extension of the rod 3 of elongation, that is to say in a manner centered on the container 1. By the expression "handle centered on the container ”, it is possible that the central axis of the handle is distant from the axis Xe of extension of the elongation rod 3, it being understood that the volume 201 of boxing interferes with the volume 30 of temporary occupation of the rod 3 of elongation.

In other words, the or one of the deformed portions 100 of the wall 10 of the container 1 is flush, between, or exceeds, the volume 30 of temporary occupation of the rod 3 of elongation inside the mold 2 This position of the deformed portion 100 results, as mentioned above, from the boxing volume 201 defined by the shape of the insert 200 and from its maximum boxing depth.

At least one of the two boxing volumes 201 of the boxing inserts 200 interferes with the volume 30 of temporary occupation of the rod 3 of elongation inside the mold 2. In other words, at least one of the two boxing volumes 201 encroaches on the volume 30 of temporary occupation of the elongation rod. As illustrated in FIG. 1, these are the two boxing volumes 201 of the boxing inserts 200 which interfere with the volume 30 of temporary occupation of the elongation rod 3 inside the mold 2.

This design is made possible by the process according to the invention, which is a stretch-blow-molding manufacturing process from a plastic preform, for example PET, within the forming unit.

With reference to FIG. 4, the method of manufacturing the container 1 comprises:

- a pre-blowing step S1;

- a blowing step S2, following the pre-blowing step S1;

- a degassing step G following the blowing step S2. In addition to the pre-blowing, blowing and degassing steps of the process, the process also includes a step of stretching the preform as well as a boxing step B of the handle using the boxing inserts 200.

The preform stretching step successively comprises a descent phase E1 of the elongation rod 3, then an ascent phase E2 of the elongation rod 3 along the extension axis Xe.

During the stretching step of the preform, the latter can advantageously be stretched so that its bottom reaches the anti-slip means of the injection point 140 of the preform.

According to the invention, and as detailed below, the ascent phase E2 of the elongation rod 3 is initiated before the blowing step S2.

Indeed, while, according to the prior art, the ascent phase E3 of the elongation rod 3 is initiated during the blowing step S2, or even at the time of degassing, the ascent phase E2 according to the invention occurs earlier during the manufacturing cycle of the container 1, in particular during the pre-blowing step S1.

More precisely, with reference to FIG. 4, the ascent phase E3 according to the prior art is initiated at an instant tE3 after the occurrence of a pressure peak P inside the container 1, occurring during the step blowing S2, illustrated on the curve C of the pressure inside the container 1 to be formed.

In addition, still according to the invention, the boxing step B is initiated during the ascent phase E2 of the elongation rod 3, after the distal end 310 of the elongation rod 3 is raised above of a predetermined height along the extension axis Xe, on which the handle is formed.

The handle can thus be formed on the axis Xe of extension of the elongation rod 3, without the phenomenon of over-stretching of the plastic material deformed by the boxing inserts 200 occurring, and without the rod 3 elongation

does not prevent boxing, the elongation rod 3 being preventively reassembled.

As shown in Figure 1, the predetermined height, along the X axis

extension, above which the elongation rod 3 must rise to initiate the boxing step B, is preferably located above a central boxing axis Xb along which the boxing inserts 200 are movable.

The central boxing axis Xb is sequent and perpendicular to the extension axis Xe of the elongation rod 3.

Figure 4 is described below according to a time sequence.

A manufacturing sequence begins at an instant to, also called the start of the cycle.

Then, after a few ms, it is the effective start of the manufacturing cycle, with the descent phase E1 of the extension rod which is initiated at an instant t-i. The elongation rod 3 then descends inside the mold to reach its low position.

During the descent of the elongation rod 3, at an instant t2, the pre-blowing step S1 is initiated. The pressure curve C illustrates the evolution of the pressure in the container 1 during this pre-blowing step S1.

After the initiation of the pre-blowing step S1, the elongation rod 3 reaches its low position at an instant t3 corresponding to the end of the descent phase E1. The elongation rod 3 remains in its low position for a period D of between 5 milliseconds and 120 milliseconds, and preferably between 20 milliseconds and 60 milliseconds.

After maintaining the elongation rod 3 in its low position for duration D, the ascent phase E2 of the elongation rod 3 is initiated at an instant t4.

The boxing step B is initiated while the pre-blowing step S1 is not completely completed, at an instant ts. At this instant ts, the elongation rod is raised to an elevation height HT from its low position making it possible to release a boxing volume 201 of the handle, the elevation height HT being above the height predetermined along the Xe axis of extension.

On rotary machines for manufacturing containers, such as those of the applicant, which include a carousel which carries several molds 2, this instant ts can advantageously correspond to an angular value in degrees called "DepBoxMin", which corresponds to the angle traversed by a mold from time to. This angular value can be determined using the following formula:

[Math 1]

in which:

the value PT10 corresponds to an angular value in degrees of arrival of the elongation rod 3 in a low position, that is to say in terms of time at the instant t3 (this is the angle traveled from G instant ti );

the value V then corresponds to the rate of ascent of the elongation rod 3 in millimeters / milliseconds, and;

- CAD is the rate of mold 2 in bottles / hour / mold.

According to an example application in which:

- PT10 would be equal to 62 °;

- HT would be equal to 100 mm;

- V would be equal to 1.29 mm.ms ¹

- CAD would be equal to 1200 bottles / hour / mold,

DepBoxMin would be approximately 72 °.

In this application example, the instant t4, which corresponds to the initiation of the ascent phase E2 of the elongation rod 3, can correspond to an angular value of 65 °. The time between instant fe and instant ts, necessary for the extension rod to reach the elevation height HT, then corresponds to 74 ms or even 7 ° (72 ° -7 °).

Thus, in carousel machines, the angular values relate to the rotation of the carousel of the forming unit and more precisely to the angular position of the mold relative to a reference position on a frame of the forming unit on which the carousel is movable in rotation.

During boxing step B, the deformed portions 100 of the container 1 enter the temporary occupation volume 30 (illustrated in FIG. 1) of the elongation rod 3 when the latter is in a low position between its descent phase E1 and its ascent phase E2. With reference to FIG. 1, the handle is thus formed by bringing two deformed portions 100 closer to the wall 10 of the container 1 and this at least up to a maximum spacing which is less than a minimum diameter (dm) of the rod 3 d 'elongation. This minimum diameter is for example 7 mm.

More specifically, preferably, the handle is formed by bringing the two deformed portions 100 closer to the wall 10 of the container 1 up to a minimum distance, called the "air gap". This air gap is less than the minimum diameter dm of the elongation rod 3.

In this way, a volume is kept between the two deformed portions 100 of the wall 10 of the container 1, and a liquid contained in the container can take place between these two deformed portions 100.

After the instant ts, the instant te occurs, which corresponds to the end of the pre-blowing step S1 and to the initiation of the blowing step S2. The pre-blowing stage can have a duration of 200 ms.

Following the initiation of the blowing step S2, the ascent step E2 of the extension rod ends at time t7.

It should be noted that the ascent of the elongation rod 3 ends before the pressure peak P is reached inside the container 1.

At time ts, the blowing step S2 ends, and the degassing step G is linked to end at an instant t9.

The blowing stage S2 lasts 1700 ms, and the degassing stage can last 200 ms.

After the end of degassing step G, at time t-io, boxing step B ends. This boxing step B thus has a duration of up to 1960 ms.

According to the present embodiment illustrated by FIG. 4, the ascent phase E2 of the elongation rod 3 and the boxing step B are both initiated during the pre-blowing step S1. According to another embodiment not illustrated, the ascent phase E2 of the elongation rod 3 can be initiated during the pre-blowing step S1 while the boxing step B is initiated during the blowing step S2 .

Still according to another embodiment, the boxing step B can be initiated using a servo-control of the ascent phase E2 of the elongation rod 3, for example using a cam.

Claims

1. A method of manufacturing a container (1) by stretch blow molding from a plastic preform within a forming unit, the forming unit comprising:

- At least one mold (2) defining an imprint of the container to be formed and comprising at least one insert (200) for boxing a handle, the or each insert being movable through a wall (20) of the mold;

an elongation rod (3) movable in height inside the mold along an extension axis (Xe) and intended to stretch the preform,

the method successively comprising a pre-blowing step (S1) and a blowing step (S2),

- the process also comprising:

- a step of stretching the preform successively comprising a descent phase (E1), and an ascent phase (E2) of the elongation rod along the extension axis;

- A boxing step (B) of a handle using the insert (s), the handle being formed by deforming at least one portion, called "deformed portion" (100), of a wall (10) of the container ,

characterized in that:

- the phase of raising the extension rod is initiated before the blowing step;

- the boxing step is initiated after the extension rod has risen above a predetermined height along the extension axis on which the handle is formed, the handle being formed on the axis d extension of the extension rod.

2. Method according to the preceding claim, characterized in that, during the boxing step (B), the deformed portion or portions (100) enter a volume previously occupied by the rod (3) of elongation in a position low between its descent phase (E1) and its ascent phase (E2).

3. Method according to any one of the preceding claims, characterized in that the handle is formed by bringing two deformed portions (100) of the wall (10) of the container (1) at least until a spacing maximum, the maximum spacing being less than a minimum diameter (dm) of the elongation rod (3).

4. Method according to the preceding claim, characterized in that the handle is formed by bringing the two deformed portions (100) of the wall (10) of the container (1) to a minimum distance called "air gap", the air gap being less than the minimum diameter (dm) of the elongation rod (3).

5. Method according to any one of the preceding claims, characterized in that the ascent phase (E2) of the rod (3) of elongation and the boxing step (B) are initiated during the pre- blowing (S1).

6. Method according to any one of claims 1 to 4, characterized in that the ascent phase (E2) of the rod (3) of elongation is initiated during the pre-blowing step (S1), and l boxing step (B) is initiated during the blowing step (S2).

7. Method according to any one of the preceding claims, characterized in that the boxing step (B) is initiated by means of a servo-control of the ascent phase (E2) of the rod (3) of elongation.

8. Method according to any one of the preceding claims, characterized in that the predetermined height is situated above a central boxing axis (Xb), along which the insert (s) (200) are movable, the central boxing axis being secant and perpendicular to the axis (Xe) of extension of the rod (3) of elongation.

9. Method according to any one of the preceding claims, characterized in that the step of stretching the preform stretches the preform until its bottom reaches anti-slip means of an injection point (140 ) of the preform, formed in the bottom of the mold (2).

10. Method according to any one of the preceding claims, characterized in that between the descent phase (E1) and the ascent phase (E2), the rod (3) of elongation is maintained in a low position along of the axis (Xe) of extension for a duration D of between 5 milliseconds and 120 milliseconds, and preferably between 20 milliseconds and 60

milliseconds.

1 1. Method according to any one of the preceding claims, characterized in that it is implemented on a rotary machine, which comprises a carousel and at least two molds, and the boxing step (B) is initiated at starting from an angular value DepBoxMin, in degrees, which corresponds to the angle traversed by a mold from an instant to, called the start of the cycle, which angular value is determined using the following formula:

in which :

- PT10 is an angular value in degrees of arrival of the elongation rod (3) (3) in a low position;

- V is the ascent rate of the extension rod in

millimeters / milliseconds;

- CAD is the rate of the mold (2) in bottles / hour / mold.

12. Forming unit for manufacturing a container (1) by stretch blow molding from a plastic preform, the forming unit comprising:

- A mold (2) defining an imprint of the container to be formed, the mold comprising at least one insert (200) for boxing a handle, each insert being movable through a wall (20) of the mold along at least one central boxing axis (Xb) up to a maximum boxing depth at which the insert defines a boxing volume of the insert inside the mold;

- an elongation rod (3) movable in height inside the mold along an axis (Xe) of extension and intended to stretch the preform according to a path of descent and ascent of the rod (3) elongation inside the mold,

13. Forming unit according to the preceding claim, characterized in that the rod (3) of elongation and its trajectory define a volume (30) of temporary occupation of the elongation rod inside the mold (2) , at least one of boxing volumes of the insert (200) interfering with the volume (30) of temporary occupation of the elongation rod inside the mold.